The present invention relates to a very rapid, non-catalytic process for hydrogenating unsaturated organic compounds that can be carried out at temperatures generally lower than previously utilized.
Hydrogenation reactions involve the addition of hydrogen whereby, for example, an alkene can be reduced to an alkane. The smaller alkanes can be obtained directly from petroleum or natural gas. Above pentane, however, alkanes must be synthesized, generally by hydrogenating alkenes. Prior art processes have generally required the presence of a catalyst along with relatively high hydrogen pressure and elevated temperature. Catalysts used in such hydrogenation of alkenes are usually heterogeneous with a solid phase of e.g. platinum, palladium or nickel. Similar catalytic processes have been used to hydrogenate unsaturated alcohols to saturated alcohols, and unsaturated esters to saturated esters.
Catalyzed hydrogenations of unsaturated organic compounds also have been carried out using transition metal hydrides as catalysts. U.S. Pat. No. 3,644,445 to Kroll, et al. discloses a transition metal carbonyl hydride complexed with an organo-metallic compound to form a catalyst for hydrogenation. A transition metal complex such as Wilkinson's catalyst Rh[(C.sub.6 H.sub.5).sub.3 P].sub.3 Cl, has been used in homogeneous processes to hydrogenate unsaturated compounds containing isolated olefinic and acetylenic linkages [Osborn, J. A., et al., J. Chem. Soc. (A), 1711-1732 (1966)].
U.S. Pat. No. 3,883,607 to Neikam describes the use of a heated transition metal hydrate, H.sub.2 MoO.sub.3 as a source of hydrogen in the hydrogenation of an olefin at elevated temperature. U.S. Pat. No. 2,856,428 to Brown discloses a method for reducing functional groups of organic compounds using alkali metal borohydride and aluminum chloride to react with the organic compound at 25.degree. C.
Non-catalytic ionic hydrogenation using organosilanes and trifluoroacetic acid has been disclosed by Kursanov, D. N., et al., Synthesis 1974, 633-651 (1974). The Kursanov, et al. method for the hydrogenation of alkenes requires a temperature of 50.degree. C., a time of at least several hours, and prohibits the use of strong acids.
The reduction of aryl and diaryl ketones to hydrocarbons by the slow addition of trifluoromethanesulfonic acid to the ketone in dichloromethane solution, followed by the addition of triethylsilane and stirring at room temperature for a few hours, is disclosed by Olah, G, et al., Synthesis 1986, 770-772 (1987).
It is an object of the present invention to provide a non-catalytic process for the hydrogenation of organic compounds quickly and efficiently. It is a further object to provide a non-catalytic method for hydrogenating highly substituted alkenes, secondary benzylic alcohols, tertiary alcohols and compounds containing strained cyclic groups. It is another object to provide a very rapid method for the hydrogenation of alkenes at low temperatures with very high product yield. It is yet another object to facilitate hydrogenation of organic compounds by metal hydrides or silanes with the addition of a strong acid to the reaction medium.